Nitrate Depletion in a Second‐Order Mountain Stream

Abstract

The amount of NO3‐N exported in a second‐order mountain stream draining a clearcut and logged mixed hardwood forest was studied over a 4‐year period. Calculations based on measurements of stream chemistry and discharge rates indicated a within‐stream depletion of NO3 from the upper reaches of the stream to the watershed outlet. Within‐stream depletion the first year of treatment was 127% of total NO3‐N discharged from the watershed outlet and declined in succeeding years after treatment to 99, 42, and 5%. Assays of the quantities of denitrifying enzymes in stream sediment samples suggested 1.7 kg N year−1 were lost via this pathway, compared with 3.9 kg N year−1 calculated from within‐stream depletion for the same time period. This study suggests sediment denitrification is a major pathway by which NO3‐N is lost. Within‐stream gaseous transformations are important when accounting for changes in N dynamics associated with forest management practices, and the measurement of only hydrologic discharge of NO3 could result in underestimation of N losses.

Pulsación diaria de la carga suspendida y disuelta en la escorrentía de fusión nival

“…El descenso de concentración al atravesar la subcuenca inferior y en la escorrentía superficial, puede atribuirse a la absorción de nitratos por algas bénticas y a la desnitrificación bacteriana en sedimentos de los cauces y áreas saturadas. Ambos factores han sido señalados, aunque la mayoría de los autores (Hill, 1981;Swank y Caskey, 1982) otorgan mayor importancia al segundo. El vertiginoso descenso de la concentración de nitratos en la escorrentía superficial (estación A) desde el invierno hasta fines de abril, pasando de 0,126 a 0,010 mg/l., sugiere la trascendencia de los procesos biológicos, dependientes de la temperatura, en la eliminación de nitratos.…”

Variation in Stream Water Quality in an Urban Headwater Stream in the Southern Appalachians

“…The effect of low surface:volume ratios is to mask the apparent significance of detrital dynamics that serve as the source of much of the ammonium in stream water. Swank and Caskey (1982) measured denitrification in sediments of a stream Season was defined as; winter (n = 18), Nov. 15-Mar. 15; spring (n = 18), Mar.…”

“…Studies of in-stream processes have focused primarily on nitrate and phosphorus depletion or retention in headwater streams. Swank and Caskey (1982) determined nitrate depletion in a typical southern Appalachian headwater stream following clear-cutting. In their study, denitrifying enzymes in sediments caused the loss of an estimated 1.7 kg N yr −1 from the watershed by converting nitrate to nitrite.…”

Forest Management Effects on Surface Soil Carbon and Nitrogen

“…Elevation ranges from 720 to 1065 m with slopes of 20 to 80%. Three vegetation community types were within the watershed: (i) cove hardwood, at lower elevations and adjacent to the stream at intermediate elevations, (ii) chestnut oak (Quercus prinus L.), at intermediate elevations on mesic southeast-and north-facing slopes, and (iii) scarlet oak-pine, at intermediate and upper elevations and ridgetops on xeric southwest-and south-facing slopes (Swank and Caskey, 1982). Before harvest, the basal area was 25 m : ha" 1 (Boring et al, 1988).…”